The Ending of the Sphere Itself [possible SPOILER]

**SPOILERS ahead**

The Sphere obviously survives the big explosion (which I think shows how advanced its technology is) in contrast to the scientists thinking of it destroyed, but it remains there the whole time the scientists are discussing what they should do/say. Only at the moment when they are forgetting it and its powers, the Sphere ascends from the ocean into the space. One could say it's either accidental, or maybe the aliens in charge of it called it back and the two events just happened at the same time. But I like to think forgetting about the Sphere and the powers it granted, and it leaving (whether by its own choice/programming or ordered by whomever it belonged to) are related. This would show that the Sphere and/or its creators had purpose in making it and sending it out into space (or leaving it for others to discover). So this sounded to me like, it was done with its purpose here - whether successful or not - and it's time to go, probably to another world.

We can also obviously see that the Sphere doesn't need to be picked up and carried away by a spacecraft. It can travel in space on its own, whether it has conscience or sensings of its surroundings (or the minds of the life forms entered into it?) or just transmits this data back to the owners, and they can call it back or send it elsewhere.

I also think that there should be many more Spheres scattered throughout the space, since sending one single Sphere in the hope that an intelligent life form in a vast space would pick it up is meaningless. Unless we consider the case that the astronauts did travel to another alien world, and either took or stole the Sphere from them and tried to bring it to the Earth! But this still wouldn't explain how the Sphere waited for 300 years, and then decided to leave only when the last group of people who entered it, didn't die but decided to forget about it and its abilities.

How do you think these points are plausible?